The present invention relates generally to brake caliper assemblies, and more specifically to a shock and vibration isolation system for brake calipers.
Since the 1960's, rail car operation and engineering have been experiencing the need for faster, safer and more light weight trains. The industry has been gaining experience in metallurgy and failure mechanisms as well as the ability to generate better definition of vibration operating environments affecting the brake systems.
The need for faster, safer trains has dictated the use of more complicated brake actuator and caliper systems. These systems usually incorporate intricate slack adjustor systems. With so many more pieces, the probability of failure due to component systems responding to a wider spectrum of damaging vibrations has become a problem.
With the advancements in vibration technology has come a better understanding of the brake component failure mechanisms. The damaging shock and vibrations can be accurately defined. To isolate these from the brake caliper and actuator, a tuneable, adjustable, isolation system is needed which will reduce the shock loading also. The present systems are not easily adjusted without an expensive and time consuming design or production modification. Many brake systems do not have any shock or vibration isolation for the calipers and actuators.
Many suspension systems address shock by isolating the calipers from the truck mounting brackets. However, even these systems do not reduce one of the major causes of brake caliper wear, fretting. Fretting is where a component is able to move or has play in it due to assembly tolerances. While the components are in the unloaded condition, namely brakes not applied, they are free to move around. In many cases, they rattle around or are responding to the ever present broad range of vibration generated by a rail car's steel wheel and stiff primary suspension systems. These never ending, continuous micro-motions are the main ingredient in fretting. Because the mating steel on steel surfaces are not heavily loaded when the brakes are not applied, moisture and oxygen can continually attack and form oxides on the mating surfaces. These continually forming oxides are then quickly removed by the fretting motions, to begin the cycle again.
Many brake systems with a shock absorbing mount between the caliper and actuator assembly require additional brackets and linkages to transmit the braking loads to the truck frame. These systems with their extra linkages and brackets are less compact and more complicated.
Thus, the object of the present invention is to provide a rattle free brake caliper mounting system.
Another object of the present invention is to provide a suspension system to reduce shock loading of the caliper and actuator assembly without the need of extra linkage to transmit the brake loads to the truck frame.
An even further object of the present invention is to provide a brake caliper system which reduces fretting corrosion of the caliper, bridge and bridge pin system.
A still even further object of the present invention is to provide a caliper system capable of fine tuning in the field.
An even further object of the present invention is to provide a brake caliper system which can be retrofitted to existing brake systems.
These and other objects are achieved by providing rigid-non metal bridge washers separating a caliper lever from the bridge, a rigid non-metal bridge bushing separating a shaft of the bridge pin from the bridge and a rigid non-metal lever bushing separating the bridge pin from the lever. This not only reduces the fretting, but provides non-metal to metal contact and reduces the oxidation and corrosion. Preferably, the bridge washer and the bridge bushing are unitary. A nonmetal spring is provided between the bridge pin and the lever to retard vibration of the bridge pin relative to the lever when the brake caliper assembly is not activated. The spring preferably includes a ring between the bridge pin and the lever and the ring is pre-loaded by the bridge pin. The ring is received in a recess of the lever bushing. A plurality of rings are spaced along and received in a respective recess in the lever bushing. The bridge washer, bridge bushing and lever bushing are preferably polymers.
The bridge bushing and lever bushing absorb shock and transmit forces between the bridge pin, bridge and lever during the initial phase of the actuation of the brake caliper assembly. The bridge bushing and the lever bushing are of material individually selected to absorb the anticipated shock during the initial phase of actuation of the brake caliper assembly for a particular system and environment. The characteristics of the spring is individually selected for retarding anticipated vibration of a bridge pin relative to the lever when the brake caliper assembly is not actuated for a particular system and environment. The spring rate of the spring, which includes a ring between the bridge pin and the lever, may be selected or varied by selecting the bridge pin outer diameter and the ring inner diameter for selection of pre-loading of the ring by the bridge pin. Also, the material and the cross section of the ring may be selected to select the appropriate spring rate of the spring.
The method of designing a brake caliper assembly includes determining the anticipated shock forces at each of the bushings during the initial phase of actuation of the brake assembly and then selecting the material to absorb the anticipated shock. Also, the anticipated vibration between the bridge pin and the lever is determined when the brake assembly is not activated and the spring rate of the spring is selected to retard the anticipated vibration.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.